1. Field of the Invention
The present invention relates to a semiconductor circuit that performs certain signal processing on an input signal.
2. Description of the Related Art
Signal processing circuits, which perform certain signal processing on input signals to provide changes to characteristic values of the signals such as, for example, phase, amplitude and frequency characteristic and output the signals thus changed, are widely used for various semiconductor circuits (hereinafter, referred to as ICs). Examples of such signal processing circuits include delay circuit, amplifier, filter and the like.
With the recent progress in the semiconductor manufacturing process, an operating voltage of an IC is steadily on the decline, and now the IC operating at a power supply voltage of about 1.5 V is mainstream. As power supply circuits for supplying suitable power supply voltages to such ICs, switching regulators such as DC/DC converters, and series regulators (also referred to as “Low Drop Outputs (LDOs)”) are used.
From the perspective of energy efficiency, a switching power supply is more advantageous than a linear regulator; however, a voltage generated by a switching power supply is superimposed with a ripple synchronized with a switching cycle of the power supply.
An amount of change provided to a characteristic value of a signal by the above signal processing circuit is sometimes dependent on a power supply voltage. For example, it is known that a delay amount of a delay circuit configured with multi-stage cascaded buffers (inverters) is influenced by the power supply voltage. If a power supply voltage for such a signal processing circuit is generated by the switching power supply, an amount of change provided to a characteristic value of the signal varies due to an influence by a ripple of the power supply voltage. That is, there occurs a problems that, in the case of a delay circuit, jitter is superimposed on a delay amount; and in the case of an amplifier, a ripple is superimposed on an amplitude of a signal.